CHEMISTRY COMMUNITY

CameronDis2K

In general, the slow step is usually the rate determining step to evaluate a k value, but in general the above comment (^) is also correct.

CameronDis2K

As the reaction proceeds, think of it as a curved graph (seen with the equilibrium reaction graph, with E), the initial rate is very high as there is a readily amount of reactant available to react, and as its used up less reactant is available, so the reaction rate goes down (as reaction rate depen...

CameronDis2K

The intermediate cancels out in the rate determining step (before the final overall equation), and is not present in the overall reaction --> as its presence in the reactant of one reaction and the product of another reaction, makes itself cancel out.

CameronDis2K

Activation energy and enthalpy (deltaH) both have the same units of Joules, and one deals with chemical kinetics (Ea) while the other (deltaH) deals with thermodynamics.

CameronDis2K

If any compound is not present in the overall reaction, then it can be considered an intermediate (as it cancels out in the reactants and products). Therefore, NO3 can be considered an intermediate.

CameronDis2K

The purpose is to find the k value of a reaction (products or reactants favored) based on activation energy, temperature, and frequency factor (“the efficiency of a collision”)

CameronDis2K

An intermediate will cancel out in the overall reaction in the end (not appear), while a catalyst is not consumed in a reaction (appears in the beginning and reappears in the end).

CameronDis2K

In adsorption, the reactants sit on top of the solution or catalyst, while absorption (as in the class example) is when water is absorbed by a sponge (so completely different meanings and uses in context).

CameronDis2K

In regards to the orientation and collision of atoms, the frequency factor, A, in the Arrhenius equation (k=Ae^-Ea/RT), represents the percentage of molecules in the reaction that actually collide to break and form new bonds (that becomes the products). Higher the A, the more likely the reaction is ...

CameronDis2K

Using the k equation: k=Ae^-Ea/RT, you take the natural log of each side, and move the exponent into the coefficient. The presence of two temperatures represents the deltaT of a reaction (as a reaction may increase or decrease in temp based on if the equation is endothermic or exothermic).

CameronDis2K

It is usually an element or compound in a series of reactions that cancels out as is not present in the overall final equation (it is consumed in the process):
A + B --> C
B + C --> E
2B + A --> E, here the intermediate is C.

CameronDis2K

A catalyst will lower the activation energy (Ea) in a reaction, causing the curve of the rxn process vs energy graph curve to be lower than without a catalyst.

CameronDis2K

NADH is involved in the cellular respiration pathway to produce ATP and is involved when NAD gains a hydrogen atom to create the biphosphoglycerate molecule (the NAD also abandons its inorganic phosphate).

CameronDis2K

Since hydrolysis represents the breaking of bonds in a reaction, energy and heat will for sure be released (as products are favored) leading to an exothermic reaction where the deltaH is negative.

CameronDis2K

The unique rate equation tells us that there is a ratio of products and reactants that is equal in terms of the rate in which the reaction is proceeding. Coefficients in the rate law relate to the coefficients of the balanced equation and shows the ratio between them.

CameronDis2K

The intermediate in a series of reactions can be identified by seeing which element is both in the products of one reaction and reactants of another (it will cancel out as they are on opposite sides). Since it is not written in the overall reaction (as it is cancelled out), it is not included in the...

CameronDis2K

Activation energy simply put is the minimum amount of energy that is required to be inputted into a reaction to move the reaction forward. In the graph/diagram of energy vs. reaction process, the 'hump' in the graph represents the activation energy.

CameronDis2K

I'm still confused as to how the equation lnk = -deltaH/RT + deltaS/R is related to a graph and what the graph shows us (extra)?

CameronDis2K

Delta G (not) is the standard state of the Gibbs free energy of a compound, usually at 1atm and 25C (temperature). Delta G by itself depends on the compounds and non-STP conditions.

CameronDis2K

So if you were given an oxidation and reduction half equation, how do you know which coefficient (in front of the 'e-') to use? Do you add the moles of e- up or just select a number?

CameronDis2K

Hi! I'm still confused on how to decide which element in a multi-element compound you chose that is apparently oxidized or reduced?

CameronDis2K

Increase in temperature yields a larger temperature change (where T2 and T1 is compared) and ther larger the temperature increase, the larger the deltaS (assuming the volume is not changing), as seen with the equation deltaS = nCln (t2/t1).

CameronDis2K

Isobaric means that deltaP = 0, but doesn't say if the process is reversible or irreversible. Therefore, the only assumption one can make is that U = detaH - pdeltaV (as there is only one P value to plug in, usually external pressure).

CameronDis2K

If the concentration isn't given then most likely you must use other presented concentrations (and the ICE table) to calculate it. But the ratio of change could be 1 (the C part of the table) which would translate as just an X, but later the quadratic solution is plugged into these values to find co...

CameronDis2K

A decrease in pressure corresponds to a higher volume (as pressure and volume are inversely proportional according to the ideal gas law, PV=nRT). So the reaction side with more moles of GAS is favored, as the higher moles of gas can occupy the larger value to return the reaction to equilibrium.

CameronDis2K

Correct, there are 3 different R values depending on the units that are presented to you, such as atm or torr. But they all are equivalent to each other (even though their units are somewhat different(.

CameronDis2K

Correct, reversible is applied to the equation W = -pexdeltaV, when the change in p is constant. The other equation is used when the process is irreversible, and usually isothermal (deltaT = 0).

CameronDis2K

most entropies will be given to us, but it can be known that a perfect crystalline structure or molecule has a delta S of 0 J/K (though in reality, this is not possible, as seen with the 3rd law of thermodynamics)

CameronDis2K

a negative delta G (corresponding to a positive delta S) correlates to a spontaneous reaction, while a positive is vice versa. If the delta G is 0, the system will have reached equilibrium, and the forward and backward rates are the same.

CameronDis2K

It represents the heat released by the system, or heat lost by the system. Therefore, it's not always -, depends on the pathway of heat transfer that determines the sign of q.

CameronDis2K

Residual entropy is calculated using the equation S=Kb * ln W --> in essence an entropy calculation based on the degeneracy of an entity. In general the higher the degeneracy the larger the S. W can be a whole # or the number of ways a molecule can be arranged.

CameronDis2K

If certain info is given, yes (but not necessarily the actual numerical value). For example, a -q can signify that heat is being lost from the system (transferred to another entity), and negative work can mean work is being done BY the system (work done ON the system signifies a positive w).

CameronDis2K

Yes, constant external pressure, as it allows the system to change somewhat independent of the external environment. For example, in the equation for an irreversible expansion work, W = - P external * delta V. However, if it is a gas in a container, pressure of the gas may be determined through the ...

CameronDis2K

For this course, it can be used to calculate entropy via the Boltzmann equation, that is S = Kb * ln W, where W is the degeneracy. In general larger molecules will have greater degeneracy. However, this equation has a lot of error associated with it, as its relying on a whole number and a defined va...

CameronDis2K

Isothermal means constant temperature, or the change in temperature = 0. For the work equations, the irreversable expansion equation can be used, which is W = - P external * deltaV.

CameronDis2K

a positive delta S can signify a spontaneous reaction, but to determine favor ability, Gibbs free energy equation must be used. But for now, positive delta S means particles are going towards disorder (more forms of degeneracy).

CameronDis2K

In most of the experiments, a closed experiment is described. However, is it ever possible to have a completely isolated system, as entropy exists and there can be very minute molecular interactions which allow very small amounts of heat, particularly, to enter or escape?

CameronDis2K

You can use either Celsius Kelvin, but the units must be consistent throughout the equation, so the specific heat constant (for the specific material) must also be in the same units as the deltaT in the equation q=cmdeltaT.

CameronDis2K

Yes, there's usually a pattern you can follow: anything with an OH- is usually a strong base (ex. KOH), and any compound preceded with an H and from the halogen group is usually a strong acid (HBr, HCl, etc.). But any compound with an NH3 is usually a weak acid, and others you can just memorize, lik...

CameronDis2K

In the ICE table, gases and aqueous (which is dissolved in H2O) solutions are included, not solids or liquids. Therefore, H2O (almost always a gas or liquid) is included only if its not a liquid.

CameronDis2K

Both represent heat energy of deltaH, but one is used when the volume is constant and the pressure changes (Qv) and the other is when the pressure is constant but the volume is changing (Qp).

CameronDis2K

The idea of balancing a reaction is not associated with K; regardless, in order to solve a chemistry problem, the reaction should be balanced (with coefficients). When it is balanced, depending if the information is given for either pressure or concentration of the reactants AND products @ equilibri...

CameronDis2K

Of course PV=nRT is labeled as the "Ideal Gas Law" - so no matter what condition of the experiment, some factors of the experiment will affect the calculations from the ideal gas law. For example, the temperature may fluctuate by +/- 0.5 C, and therefore a solid temperature may not be reco...

CameronDis2K

It is part of LeChatlier's Principle: adding heat to a reaction will favor the other side of the reaction (wherever "heat" is added- reactant or product side). Exothermic reactions have "+heat" on the products side, therefore increasing the heat (or adding more heat) will favor t...

CameronDis2K

I believe no, but the idea of a polyprotic acid is that it can donate more than one hydrogen atom in the equilibrium reaction (like 2+, 3+, etc.) and therefore will have different ionization levels and multiple Ka values.,

CameronDis2K

Increasing the pressure will in turn decrease the volume of the container in which the specimens are contained: the side with less moles of gas favored as there are fewer molecules on that side of the reaction = smaller volume.

CameronDis2K

Always study like you are genuinely learning for fun and not for a test (but be serious). While taking the exam, don't see it as an exam, but as a homework problem thinking you are able to just spill out your ideas... you don't need to be perfect/cookie cutter when answering or thinking about the pr...

CameronDis2K

I believe because its the same ideology like adding an extra compound or atom that's different/not in the original equilibrium equation, will not change the K value or the reaction process. No shift occurs and it will be like the original equilibrium conditions.

CameronDis2K

One use is when a compound or reaction is not in the STP state (standard 1atm, 25C), and you need to find a certain value to plug into a stoichiometric equation. More for specialized cases...

CameronDis2K

How do we know what type of acid/base a compound is? Such as bronstead-lowry, or arrhenius, or lewis acids/bases? And based on this categorization, do we treat it differently in a problem?

CameronDis2K

How can you tell based on the chemical formula of a compound that it is a strong or weak base? Like I know my memory HCl and CH3COOH as strong and weak, respectively, but don't really know any others.

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